In general, a sampler that samples a soil sample for site investigation is classified variously depending on operation principle, sampling method, and pipe structure, and the like. Undisturbed samples are mainly sampled for the mechanical experiments such as consolidation test, permeability test, shear strength test, and the like, which are conducted on soft soil. In addition, samplers have been developed in various manners in terms of size and function to take such soil samples. However, a fixed piston type sampler is used mainly in that it is not limited in sampling depth, its operation is relatively simple, and good quality samples can be sampled.
Meanwhile, a free piston sampler is disclosed in that since a piston is not securely fixed to the piston type sampler when the press-in operation is performed and thus a friction between a sample and a sampling tube is large, it is difficult to take a sample but a device for preventing detachment of the sample is provided. In addition, a fixed piston type sampler is disclosed in which its structure is the same as that of the free piston sampler, but the recovery rate of samples can ensured up to 100% owing to a piston fixed thereto such that a correct sampling operation is possible and the sampler is effective in soft clay. By virtue of such advantages of the fixed piston, it is recently used mostly in a construction field. Examples of such a fixed piston type sampler include a hydraulic type piston sampler (ASTM D 6519-05, 2009) and a mechanical type piston sampler (JGS 1221-1995).
Korean patents associated with site investigation employing drilling equipment such as a piston type sampler are as follows:
First, Korean Patent Registration No. 10-0419257 entitled “METHOD AND APPARATUS FOR AUTOMATICALLY PERFORMING STANDARD PENETRATION TEST” is disclosed. In this patent, only a hammer is caused to drop on a ground in a state in which the hammer is lifted mechanically such that an additional penetration due to a drop impact or a loaded load is prevented while maintaining a constant drop height when striking the hammer by a free drop, thereby enabling penetration of a sampler by a correct strike, preventing the erroneous operation of a worker through the automatic measurement of the numbers of strikes of the hammer each time the hammer is struck, and making it possible to determine whether the test continues to be performed or is suspended through the automatic measurement of the amount of penetrations of the sampler to calculate the number of strikes as a final result. In addition, a method and apparatus for automatically performing a standard penetration test (SPT) is suggested which includes a control device for recording and outputting a test result while helping perform the test in a blanket and automatic manner by controlling the driving of the devices such that a correct test result can be obtained.
Second, Korean Patent Registration No. 10-0355400 entitled “VERY LARGE DIAMETER (VLD) SAMPLER” is disclosed. In this patent, disturbance of soil can be minimized and a large-scale undisturbed sample having a diameter of more than 300 mm in various depths can be sampled in a natural sample sampling process for correctly evaluating the engineering characteristics of a soft ground as a criterion of the review of constructionability, stability, and economic efficiency in a construction work in a river or offshore area where the soft ground is distributed.
Third, Korean Patent Registration No. 10-0356283 entitled “LARGE DIAMETER SAMPLER ENABLING UNDISTURBED SAMPLES TO BE GATHERED” is disclosed. In this patent, high-quality undisturbed samples can be gathered even in a clay or loamy sand ground upon the site investigation such that the gathering of the undisturbed samples is possible which can obtain more correctly the parameters of the ground necessary in the basic design of a structure.
Fourth, Korean Patent Registration No. 10-0768686 entitled “PICKING APPARATUS OF A SOIL SAMPLE” is disclosed. In this patent, the apparatus is configured in a simple structure such that a strike rod for striking a ground is lifted and freely drops periodically by rotating a pair of rollers to take a soil sample.
As discussed above, the conventional prior arts suggest large diameter samplers with a diameter of 30 cm or more (see the second and third patent documents) which does not employ a sampling tube like the piston type sampler, or samplers (see the first and fourth patent documents) for taking disturbed samples. That is, the patent techniques associated with the piston type sampler mainly used in a construction field are not suggested or taught.
The advantages and disadvantages of the fixed piston sampler presently used will be discussed hereinafter.
Among the fixed piston type samplers, the hydraulic type piston sampler has an advantage in that assembly, operation, disassembly, and use thereof is easy, but still entails several disadvantages in that there is a limitation in the control of the advancement speed and the advancement of the sampler, and in that “a vacuum removing valve” needed when separating a piston from the sampling tube containing a sample is not included in the sampler. In addition, the mechanical type piston sampler has an advantage in that it can satisfy the requirements for a multi-purpose sampler more fully as compared to the hydraulic type piston sampler, but encounters a disadvantage in that its manipulation is complicated and sampling costs are expensive. That is, the hydraulic type piston samplers widely used in Korea have a problem in that its manipulation is easy but the quality of a sample is deteriorated. Also, the mechanical type piston samplers used rarely has an advantage in that good quality undisturbed samples can be obtained, but still a problem in that its manipulation is difficult and much time is spent to manipulate the samplers.